This invention relates to piston and ring assemblies and particularly to assemblies having rings that use fluid pressure to increase the expansive force of the rings against cylinder walls of reciprocating engines and pumps in which they are used.
Conventional rings are substantially rectangular in cross section and depend on tension of their material for expansion to maintain pressure of the circumferential surfaces of the rings against their cylinder walls during the complete cycles of the operation of the pistons. The prevention of flutter of the rings at high speeds of operation of internal combustion engines may determine the maximum tension required. Because of the high tension required in high-compression, high-speed engines, the rings must be fabricated from alloys that are more expensive than cast iron. The tension required to prevent flutter and the resulting blowby and loss of lubricating oil is often sufficient to cause excessive wear of the rings and the cylinder walls. To decrease the rate of wear, the outside surfaces of rings are conventionally treated with various metals and oxides.
Various shapes of rings and grooves have been disclosed to cause forces other than that from expansive tension to be applied during at least a portion of each operating cycle to help provide a seal between the piston and the cylinder walls. None of these structures have been generally adopted in place of conventional rectangular rings similar to those that have been in use for a long time. The different forces, including the substantial forces from combustion and the changing inertial forces at high speeds, in a reciprocating internal-combustion engine are changing rapidly during a cycle of operation. The structure that provides forces to supplement favorably the inherent expansive tension of rings during one part of a cycle may be detrimental at another part of the cycle. When the rings and grooves of a piston are complicated in structure, the cost of manufacture would obviously be increased.